Reading voltage with no connection at relay

Hi everyone. I am using 34970A data acquisition with 34901A 20 channel multiplexer. I have done the remote command using C# to get the data/value. Question: How do I get the voltage value remotely using C# without getting error when there is no connection to the relay inside the multiplexer? How do I tell the system to return 0V and not reading error when there is no connection to the relay inside the multiplexer?